1. Field of the Invention
The present invention relates to a sealing device for preventing water from leaking through a joint constituted by the coupled surface of a civil engineering component such as a shield segment, a concrete product for a manhole, a culvert, and so forth.
2. Summary of the Related Art
A shield tunnel excavated in the ground of an urban area is made of a large number of concrete segments 1 formed as modules to constitute the inside surface of a portion of the tunnel, as shown in FIGS. 1 and 2. At the time of the building of the tunnel, the segments 1 are closely coupled to each other both in the circumferential direction a of the tunnel and in the longitudinal direction b thereof. Each of the segments 1 has front and rear flanges 2 and 3 extending in the circumferential direction a of the tunnel and located on two of the four edges of the body of the segment, and upper and lower flanges 4 and 5 extending in the longitudinal direction b of the tunnel and located on the other two of the four edges, so that the segment is formed as a container. When the segments 1 are coupled to each other, the mutually adjacent flanges 2 and 3 thereof are laid on each other and then are tightened together by coupling bolts 6, and the other mutually adjacent flanges 4 and 5 of the segments are also laid on each other and then are tightened together by other coupling bolts 6.
Since it is necessary to seal the joint of the mutually coupled surfaces of the mutually tightened flanges in order to prevent spring water from leaking into the interior of the tunnel, a band-like seal 8 is secured to at least one of the mutually coupled surfaces facing the gap 7 between the surfaces. The seal 8 is made of a conventional water-expansible material such as a mixture which includes a highly water-absorbing resin and a synthetic rubber and is subjected to forming and vulcanizing. The seal 8 is formed as a single layer of the material. When the water W enters the gap 7, the seal 8 of the single layer is expanded with the water, thus sealing the gap so as to prevent the water from leaking into the interior of the tunnel through the gap.
However, since the water-expansible material is less tenacious and elastic than an ordinary water-unexpansible rubber, the thickness of the seal 8 needs to be larger in order to prevent the water from leaking into the interior of the tunnel through the gap 7 before the seal absorbs the water and is expanded therewith. For that reason, not only is the cost of the seal 8 increased, but also it is likely that the projecting surface of the seal will collide with other components of the tunnel, and cause the seal sticking surface of the flange of the segment 1 to drop off during conveyance or the like. This is a problem.
When the seal 8 is expanded with the water W, the sealant becomes much less tenacious. The expansion takes place in three dimensions. In particular, the sealant 8 expends by a relatively greater amount in the longitudinal directions of the gaps 7 extending between the segments 1 in the circumferential and longitudinal directions of the tunnel. For that reason, if the mutually adjacent segments 1 become displaced because of vibration or the like, the expanded seal 8 can break or crack in part, or can separate from the seal sticking surface of the flange of the segment and drop off. This also is a problem.
In order to solve the problems mentioned above, the present inventor proposed a combined seal 9 shown in FIGS. 3(A) and 3(B) and composed of a water-expansible material and a water-unexpansible rubber, and conducted various experiments and studies on the seal. A similar seal is disclosed in copending, commonly assigned application Ser. No. 07/629,173. The seal 9 includes a band-like expansible central portion 10 made of the water-expansible material, and unexpansible lateral portions 11 made of the water-unexpansible rubber and extending on both the side surfaces of the central portion.
When the gap 7 which is formed between the flanges 4 and 5 of segments 1 and in which the seal 9 is provided is at the initial stage of spreading as shown in FIG. 3(A), water W comes into contact with only the unexpansible portion 11 so that it takes some time for the water to enter into the expansible portion 10 to expand it to stop the water. For that reason, there is a problem that the water W is likely to leak through the gap 7 along the seal 9 at the initial stage of spreading of the gap. FIG. 3(B) shows the later state of spreading of the gap 7. When the expansible central portion 10 is expanded with the water W, the portion pushes and moves both the lateral unexpansible portions 11. For that reason, there are problems in that the restriction of the displacement of the seal 9 in the direction of the width thereof is less than that of the displacement in the longitudinal direction thereof, and the stuck bottom of the seal 9 is likely to separate from the segment.